Justification and implementation of the layer thickness control method in ultrasonic spraying

Abstract

Relevance. The need for the development and widespread use of the ultrasonic spraying method, which has unique advantages, to solve the most pressing problems of modern industry. In particular: minimal, of all known methods, energy consumption for the implementation of the process, the possibility of forming fine droplets without the use of gas under pressure, regulating the dispersion of the formed aerosol by the parameters of the emitter, etc. However, for widespread practical use of the ultrasonic spraying method, it is necessary to ensure spraying conditions with a specified dispersion and productivity. In this regard, there is a need to develop a method for controlling and maintaining the necessary and sufficient thickness of the liquid layer on the surface of the piezoelectric transducer of the atomizer, the spraying of which will ensure, at a given spraying performance, the formation of an aerosol with the smallest deviation in the size of the formed droplets relative to the average value. It is proposed to control the thickness of the liquid layer by identifying the dependence of the resonant frequency of the piezoelectric transducer of the atomizer on the thickness of the liquid film on the oscillating surface of the atomizer. Aim. To develop a method and means for controlling the thickness of the layer of sprayed liquid by changing the resonant frequency of the ultrasonic oscillatory system and maintaining the optimal value of the layer thickness by changing the amplitude of vibrations of the surface of the ultrasonic sprayer. Objects. Liquid atomizing with ultrasonic high-amplitude vibrations. Methods. Obtaining the frequency characteristics of ultrasonic oscillatory systems, analyzing changes in the amplitude-frequency characteristics of oscillating systems and identifying criteria that allow monitoring and managing the ultrasonic spraying. Results. The authors have proposed and developed the method for indirectly monitoring the thickness of a sprayed liquid layer on the oscillating surface of an ultrasonic atomizer, based on measuring the resonant frequency of an ultrasonic oscillating system. The possibility of implementing the method and its practical application is caused by the fact that in the working range of layer thicknesses of the sprayed liquid, the change in the resonant frequency can reach 100 Hz, and with a frequency measurement accuracy of 1 Hz, the accuracy of determining the layer thickness will be no more than 2% of the working layer thickness. The identified dependencies and certain values of possible ranges of changes in the controlled parameter made it possible for the first time to develop a method for automatically controlling ultrasonic spraying, ensuring the maintenance of optimal modes of ultrasonic influence (amplitude of vibrations of the spray surface) and the thickness of the layer of sprayed liquid.

Keywords

• ultrasonic spraying
• aerosol
• capillary waves
• resonant frequency
• ultrasonic oscillatory system